Fabricating electrical circuit matrix including magnetic elements



Oct. 12, 1965 D. c. WENDELL, JR 3,2 0,

FABRICAIING ELECTRICAL CIRCUIT MATRIX INCLUDING MAGNETIC ELEMENTS 7 Original Filed Sept. 13, 1955 2 Sheets-Sheet 1 mass IN VEN TOR.

DOUGLAS C. WENDELL,JR.

Oct. 12, 1965 D. c. WENDELL, JR 3,210,828

FABRICATING ELECTRICAL CIRCUIT MATRIX INCLUDING MAGNETIC ELEMENTS Original Filed Sept. 15, 1955 2 Sheets-Sheet 2 ADDRESS- SELECTING DEVICE HORIZONTAL SWITCHING CIRCUITS VERTICAL SWITCHING CIRCUITS TIMING AND READ- IN CONTROL VERTICAL PULSING HORIZONTAL PULSING CIRCUITS READ'OUT GATING CIRCUITS READ-OUT UTILIZATION DEVICE 33 IN VEN TOR.

4 DOUGLAS C. WENDELL,JR.

United States Patent 3,210,828 FABRICATING ELECTRICAL CIRCUIT MATRIX INCLUDING MAGNETIC ELEMENTS Douglas C. Wendell, .IL, Malvern, Pa, assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan Original application Sept. 13, 1955, Ser. No. 533,987, now Patent No. 3,005,977, dated Oct. 24, 1961. Divided and this application Oct. 20, 1961, Ser. No. 146,629 15 Claims. (Cl. 29-1555) This application is a division of application Serial No. 533,987, filed September 13, 1955, now US. Patent No. 3,005,977.

This invention relates to methods of fabricating an electrical circuit matrix having magnetic elements at the coordinate positions of the matrix. The method of the invention is especially useful in the production of magnetic memory matrices utilizing coincident current selection of bistable ferromagnetic elements in which bits of information are to be stored and read out.

In forming devices such as inductance elements, transformers, and magnetic storage elements it is customary to prepare one or more coils by winding numerous turns of wire upon an insulating form, after which a leg of the magnetic circuit is slipped through this coil assembly and joined to the remainder of the magnetic circuit by some means which avoids excessive air gap therein. The magnetic circuit may be made up, for example, of a stack of laminations, or it may be made of a wound strip, or a coherent body of compressed small particles, the wound strip or body being cut open or otherwise made in two pieces which are joined together after assembly into the coil structure. Alternatively, the magnetic core structure may be formed first by winding magnetic strip in a continuous loop or by compacting a toroid of magnetic powder, after which special coil- Winding machines are used to fabricate a coil around the open-centered core so that each turn of the coil passes through the center of the core. Toroidal cores of coherent particles also have been coupled to electric circuits by passing a number of small wires very loosely through the center of the toroid. Magnetic elements of these types may be quite useful as reactors, transformers, or memory elements; however, such methods of construction involve either a bulky coil structure or one quite difficult to fabricate, or else involve a very tedious threading operation to place the conductors within the core. In many cases the practice of winding either core or coils upon a form or otherwise prefabricating a toroidal core may give a satisfactory element, but such elements nevertheless miss by far the achievement of the most compact possible electromagnetic elements.

Another form of electromagnetic circuit element old in the art is the continuously loaded submarine telegraph or telephone cable. Such a cable may be loaded inductively by providing a central conductor with a helical serving of a magnetic alloy. Ordinarily the pitch of the helix is equal to the width of the alloy strip so that the helix lies flat in one thickness, although two servings may be employed, one over the other. This arrangement provides a single conductor closely coupled to the magnetic covering upon it, but does not provide such close coupling of a plurality of insulated conductors to the same magnetic circuit, nor is the magnetic circuit ever equipped to operate anywhere but in its unsaturated linear range, which is the only range useful for communication purposes.

In assembling multi-conductor magnetic elements in a matrix configuration, it has become customary to form individual toroidal cores of magnetic strip or of 3,210,828 Patented Oct. 12, 1965 ice fired magnetic ferrite ceramic material and to thread each conductor of the matrix through all of the cores mounted in one row, column, or diagonal at a single pass. In practice this requires that the holes in the toroidal cores be very much larger than the total cross sectional area of the wires to be passed through them, and the assembly operations still are tedious and expensive. Alternatively, coils have been wound directly on the magnetic material of each core, after which each core is mounted in a suitable structure, and each end of each coil then connected to a coil of an adjacent core or to a terminal conductor on the matrix structure. With either known method the operations of assembling and wiring the matrix are lengthy and costly, and very close coupling between the electrical and magnetic circuits is seldom if ever realized.

It is an object of the present invention, therefore, to provide a new and improved method of fabricating an electrical circuit matrix including a plurality of magnetic elements which avoids one or more of the disadvantages of the prior art methods.

It is another object of the invention to obtain much greater ease of manufacture and assembly of electrical circuit matrices such as magnetic storage matrices, furnishing matrices distinguished by simplicity of structure and close electromagnetic coupling within the magnetic elements at each coordinate position of the matrices.

It is a further object of the invention to provide a new and improved method of fabricating an information storage matrix, including a conductor network with bistable magnetic elements at the coordinate positions in the matrix, which avoids the necessity of forming magnetic core elements and thereafter making individual electrical connections from one magnetic core to another.

It is still another object of the invention to provide a novel, rapid, and efficient method of fabricating magnetic memory matrices having easily switched magnetic elements with highly rectangular hysteresis loop characteristics.

In accordance with the invention, the method of fabricating an electrical circuit matrix including a plurality of magnetic element stations at coordinate positions of the matrix comprises forming a network of mutually insulated conductors for the matrix, including the gathering together of certain ones of these conductors in groups at the stations of the matrix and the arranging of these conductors between the stations so that substantially all of the conductors are common to a plurality of the stations and so that the groups of conductors are made up of a multiplicity of different predetermined combinations of conductors corresponding to individual ones of the stations, and thereafter forming a core element of ferromagnetic material surrounding each of the groups of conductors at the individual stations of the matrix.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings,

FIG. 1 is an enlarged perspective view of a coupled circuit magnetic element constituting one of the bistable state magnetic storage elements fabricated in accordance with the invention;

FIG. 2 is a cross-sectional view taken transversely through the center of the element depicted in FIG. 1;

FIG. 3 is a graphical representation of a magnetic field-magnetic flux hysteresis loop characteristic such as may be found in the magnetic cores of the magnetic elements fabricated in accordance with the invention;

FIG. 4 is a plan view, partly in schematic and block diagram form, of a magnetic memory matrix fabricated at least in part in accordance with the invention, including a number of such magnetic elements, and including in block form the associated circuit equipment for effecting the read-in and read-out operations;

FIG. 5 is a plan view of several magnetic elements as fabricated; and

FIG. 6 is an enlarged perspective view of a modification of the magnetic device illustrated in FIG. 1, the element represented in FIG. 6 being a bistable state magnetic storage device having a simplified conductor arrangement utilizing a single wire.

Referring now to FIG. 1, there is illustrated in a modified perspective view a coupled circuit magnetic element preferably having the characteristics of a bistable state magnetic storage element and including an electrical conductor unit which is made up of at least one conductor and which is arranged compactly for a portion of the length of the unit. This conductor unit might be made up of a single conductor; in any case excessive kinking of the conductor or conductors should be avoided so as to provide a compact arrangement over which a magnetic core may be assembled closely and preferably contiguously in the manner discussed hereinbelow. A bistable magnetic element as described hereinbelow but having only a single coil or conductor can be used for information storage purposes, read-out being effected through the same coil or conductor used for switching the core of the element. However, it is preferred to provide a conductor unit suitable for accommodation of the circuit arrangements conventionally found in coincident current magnetic memory matrices employing many magnetic elements, in which case at least two coincident current coils and one read-out or sensing coil usually are provided for each core.

Thus, in its preferred form as illustrated in FIG. 1, the bistable state element is a coupled circuit magnetic element comprising a conductor unit made up of a plurality of elongated, mutually insulated electrical conductors 11, 12, and 13 extending substantially straight and parallel for a portion of their lengths in a compact bundle. Each of these conductors is surrounded by a nonconductive coating or film of insulating material, not shown in FIG. 1 but indicated at 14 on each conductor in FIG. 2. The films 14 may be, for example, the ordinary enamel or plastic coating provided on wire used in winding coils. Since these conductors are not separate turns of a single winding but instead are individually insulated and electrically distinct from each other, each one is suitable for connection in a separate electrical circuit. It may be desired to include fewer or more than three conductors, and in some cases two of these conductors might be in the same circuit, forming in eifeet a single conductor, but in any case at least two of the conductors arranged in the compact bundle are insulated from each other whenever it is desired to have in the conductor unit two separate circuits coupled to the same magnetic core.

A sleeve 16 of a thin strip of ferromagnetic material is wound compactly for more than one turn on the compact bundle of conductors 11, 12, and 13 making up the conductor unit. The sleeve 16 surrounds the bundle of conductors along at least part of the compact straight portion thereof. While the ferromagnetic strip might be wound helically, a magnetic circuit of lower reluctance ordinarily is obtained by winding spirally, each turn over the preceding one, so that only a very small effective air gap is obtained where the magnetic circuit is completed from one turn to the next.

With this arrangement of the magnetic sleeve wound on the compactly aranged portion of the length of the conductor unit, each of the conductors 11, 12, and 13 protrudes from opposite end portions of the sleeve 16, and the corresponding ends of at least two of the mutually insulated conductors, and of all three of them in the FIG.

'1 arrangement, are separated and spaced apart from each other at the end of the compact straight portion of the conductor unit. Thus the conductors are available for external connections individually into a plurality of circuits, as will be illustrated hereinbelow in connection with the arrangement shown in FIG. 4. The separation of the conductors by bending two of them at both ends of the compact straight portion may be observed in the view of FIG. 1.

A typical compact arrangement of the conductor unit and the sleeve 16 is illustrated in FIG. 2. When the conventional round wire conductors are used, it is unavoidable that spaces exist between the wires even though substantially continuous, and with wires of small diameter even the thinnest possible insulation layers 14 often take up a substantial portion of the cross-sectional area. However it should be noted in FIG. 2 that the metallic wires 11, 12, and 13 nevertheless account for a large fraction, of the order of half, of the area within the magnetic core 16. The construction of the element will be seen to give the most compact assembly of separate circuit conductors possible without resorting to unusual, and hence expensive, conductor shapes and sizes and insulating techniques. When there are many conductors, closer packing may be obtained with conventional circular-section conductors by making some of the wires of relatively smaller diameter, so that they fit in the spaces between the other wires. Ordinarily, however, the improvement in operation obtainable in this way does not justify the additional care needed to assemble the conductors in the required closely packed relationships. Thus substantial deviations are permissible from the most compact arrangement possible, while nevertheless keeping the bundles of conductors substantially free of nonconduetive spaces, except for the aforementioned gaps made unavoidable by conductor cross-sectional shape and by the insulating coatings on the conductors, and thus quite compact; this may be accomplished, of course, by arranging the bundle of conductors within the magnetic core so that, throughout the length of the bundle, each insulated conductor lies substantially in contact with the conductors nearest thereto in the bundle. One alternative arrangement of the wires involves twisting the conductors together moderately, and this often facilitates assembly since the wires do not tend to separate from each other Where they are bundled and twisted together along the straight portion of the conductor unit. The wires are considered to be substantially straight, parallel, and compactly arranged even though twisted around each other moderately tightly.

In one example of a magnetic element of the type illustrated in FIGS. 1 and 2, the individual wires 11, 12, and 13 were lengths of conventional flexible coil-winding wire having a diameter of about 0.006 inch with insulating coatings about 0.0005 inch thick. The strip or tape of ferromagnetic material was approximately 0.000125 inch thick and was wound spirally for between about five and ten laps around the three wire conductor unit. With elements of the dimensions given above the sleeve portion has a maximum over-all diameter of about 0.020 inch and conveniently has a length of about 0.125 inch, while the wires may extend, say a half inch from each end of the sleeve. Although the wound strip should form a sleeve which fits quite snugly around the conductors, the fragility of such thin strips makes it undesirable to exert during the fabrication of the sleeve sufficient tensions or pressures to make the sleeve adhere very closely to the contours of the conductor unit, and very desirable operating characteristics can be obtained without extremely tight winding. Accordingly, minor bulges and wrinkles in the sleeve are permissible. A thin, tightly applied serving of a thin, tough insulating tape directly over the wires and under the magnetic sleeve may be desirable in some cases for mechanical and electrical protection of the wires and core. It is evident, though, that the sleeve-like portion 16 effectively constitutes a length of ferromagnetic material which exhibits a strip-shaped configuration and which extends continuously and closely around the conductor unit as a contiguous layer or serving for a distance substantially longer than the periphery thereof. Preferably the sleeve portion is constituted by a strip wound around the periphery of the conductor unit for the specified distance, thus making more than one turn as in a spiral. The strip-shaped length is supported by, and lies closely adjacent to, a substantial portion of the surface of each of the insulated conductors which occupies a peripheral position in the conductor unit, as may be seen in FIGS. 1, 2, and 6 of the drawings where the number of conductors shown is small enough that each one occupies a peripheral position. In other words, the core strip extends in wound conformation continuously and closely around, and directly on, the conductor unit.

Nevertheless, in spite of the deviations from perfect compactness which are permissible in both the conductor unit and the sleeve, it will be appreciated that an extremely compact arrangement of the conductor and of the magnetic circuit arranged in close proximity thereto is achieved by the arrangement described. A great advantage of this arrangement is that the magnetic circuit approaches the minimum possible reluctance, due to the small average circumference of the flux path, and the highest possible magnetic field for a given current, due to its very close proximity to the conductors. It is extremely difiicult, if not impossible, to approach these conditions of minimum reluctance and minimum driving current with a core which is preformed before the linking conductors are assembled, which is the necessary procedure, for example, when the core is formed by pressing small particles and sintering.

The bistable state magnetic storage element requires for its satisfactory operation that the thin strip, after forming into the sleeve 16 to'provide a generally toroidal magnetic flux path which is linked with the magnetic fields associated with any current flow through the conductor unit, have a suitable bistable state magnetic field-magnetic flux hysteresis loop characteristic. To be suitable for that purpose this magnetic field intensity-flux density characteristic not only should be such that its retentivity value is a large fractionusually more than half and preferably more than 0.9of its saturation flux density, but also should be such that, when the ferromagnetic material of the sleeve is given a remanent flux density approaching its retentivity value in one sense of magnetization, this remanent flux density is not changed substantially by a substantial magnetic field intensity in the opposite sense, While an intensity not over several times that substantial field intensity-usually less than 4 or 5 times as great and preferably less than twice as great switches the material of the sleeve to its other stable magnetic state by producing a remanence approaching the aforementioned retentivity value but in the aforesaid opposite sense.

From the representative hysteresis loop characteristic depicted by the solid line curve in the graph of FIG. 3, it may be observed that a magnetic field-magnetic flux characteristic satisfying these requirements has two well defined, relatively steep flux-switching region 24 to 21 or regions 21 to 22 and 23 to 24, each preceded by a Well defined, relatively steep flux-wsitching region 24 to 21 or 22 to 23 respectively. The hysteresis loop has the usual coordinates, with magnetic field intensities in two senses, arbitrarily designated positive and negative, along the abscissa and corresponding magnetic flux densities along the ordinate. To plot the loop the core is symmetrically cyclically magnetized, using a magnetic field having an amplitude sulficient to cause the flux to approach the saturation condition. In fact, the curves in FIG. 3 are obtained by using a maximum field intensity 26 such that the point 21 corresponds to saturation flux density 27. The point 28, where the curve crosses the vertical axis, then represents the retentivity of the core.

Now, application of a predetermined substantial magnetic field 29, in the opposite sense, does not change substantially the remanent flux density, which returns practically to the point 28 when the field 29 is removed. In other words, the portion of the loop between 28 and 22 represents a substantially reversible region in the magnetic characteristic, and variations over this region are accompanied by only negligible hysteresis losses. This will be recognized as a generally necessary condition for utilization of the magnetic elements in coincident current magnetic memory matrices. However, application of a magnetic field 26 in the negative sense, having the same magnitude as the positive field 26, produces saturation of the flux density in the negative sense, after which the flux density returns to its negative retentivity value 31. As the negative magnetic field is applied, the material passes through the zero flux condition 32, respectivel the coercivity value of the material.

A hysteresis loop characteristic of the type represented by the solid line curve in FIG. 3 may be obtained by the use of a number of magnetic materials known to the art. In the usual case it is desirable that this type of characteristic be obtained without annealing the material after it is wound into the form of the sleeve 16,

because the conventional enamel or plastic insulating coating is, of course, unrefractory and incapable of resisting high temperatures. Alternatively, an inorganic, for example vitreous, insulating material may be used on platinum or other conductors capable of resisting high temperatures, permitting annealing the wound sleeve at high temperatures.

A characteristic of the type represented approximately by the solid curve in FIG. 3 may be obtained, for example, with an unannealed iron material containing 5% silicon. It will be observed that the retentivity value 28 is a large fraction, and more specifically more than half, of the saturation flux density 27, and further that the application of the substantial field intensity 29 in the reverse sense does not change substantially the remanent flux density, which returns substantially toits retentivity value 28, while an intensity 26' which is equal in magnitude to the positive field intensity 26 and suflicient to saturate in the negative sense is not more than several times the intensity 29, and more specifically is less than 4 or 5 times the value 29.

Ordinarily, considerably more rectangular hysteresis loops are available than that of the solid line curve in FIG. 3, although the latter will provide satisfactory operation in certain coincident current memory systems. A material preferred for incorporation in the magnetic elements of the present invention has the approximate composition of 4% molybdenum, 79% nickel, and the balance primarily iron. This is an alloy which, when annealed after working, commonly is known as a Permalloy. However, for these elements it is not necessary that the material be annealed after the rather heavy rolling op eration which provides the thin strip. It is remark able that this alloy composition provides a highly rectangular hysteresis loop, as indicated by the dashed line curve in FIG. 3, even though not annealed after the strip has been prestressed with the production of unrelieved internal mechanical strains caused by rather drastic cold working. The unannealed condition in the present usage refers to the omission of annealing after final rolling of the strip and especially after the application of the magnetic material around a conductor unit, it being obvious to those familiar with the production of very thin rolled metallic sheet and strip that the conventional annealing nevertheless may have been resorted to after at least the initial reducing passes through a rolling mill to preserve the mechanical integrity of the strip regardless of its magnetic characteristics. The retentivity value is indicated on the dashed line curve at 23', and the re tentive flux-storing regions 21 through 28' to 22' and 23 to 24' (through the negative retentivity point 31') are remarkably flat for an unannealed material, while the flux-switching regions following 22' and 24 are very steep. Thus, the retentivity value 28 is more than 0.9 of the saturation flux density 27, while a predetermined reverse field intensity 29' may be applied which has a magnitude more than half of the value 26' required to approach saturation density without changing the remanent flux density substantially; a wound strip core having magnetic properties satisfying these requirements of retentivity and of the ratio between reverse magnetic field intensities in the substantially reversible region and the intensity required for substantial saturation may be defined, for the purposes of the present specification and of the appended claims, as having an essentially rectangular magnetic hysteresis loop characteristic. A rectangular loop characteristic is the same as a square loop characteristic, depending only on the arbitrary choice of scales for representing the units of magnetic field strength and magnetic flux in the graphical representation of the hysteresis loop. With any of the materials mentioned it is recommended to make the strip thickness of the order of 0.001 inch or less to give the desired magnetic properties using the pulsed wave forms ordinarily encountered.

FIG. 4 shows in plan view and partly schematically an electrical circuit matrix including a plurality of magnetic element stations at coordinate positions in the ma trix. This matrix is shown in its preferred form of a magnetic memory matrix arranged upon an insulating support 41, with which are associated various circuits, shown in block diagram form, for utilizing the matrix as a coincident current magnetic memory. The support 41 conveniently can be made by printed circuit techniques, starting with a laminate having, for example, a phenolic-impregnated base and a thin copper foil firmly aflixed to the upper surface of the base. Much of the copper foil is removed during the etching operation to leave numerous islands 42, 43, and 44 in the central, marginal, and corner regions respectively of the support 41, as illustrated in FIG. 4. These conductive areas may be tinned by dipping in solder before assembly of the matrix, since they are to serve as areas for solder interconnections of the various magnetic elements and external wiring connections to the circuits associated with the array.

As illustrated, the array is a three by three matrix, although it will be understood that much larger matrices, such as 16 by 16 or 100 by 100, or 256 by 256, may be provided, as desired, or that the matrix might be a rectangular rather than a square array. The illustrated matrix includes nine bistable state magnetic storage elements, each similar to the element illustrated in FIGS. 1 and 2 suitable for a double coincidence read-in system with one read-out circuit.

More specifically, the matrix is made up of a network of insulated read-in and read-out conductors, gathered together at each of the nine stations of the matrix in a compact bundle of substantially straight lengths of the conductor. Thus, referring to the station in the matrix common to the upper row, which may be designated the first row, and to the left column, which may be designated the first column, there is shown schematically a read-out conductor 11 and two read-in conductors 12 and 13. Between this and the other eight bundles of substantially straight lengths of conductors the network of conductors is arranged in a configuration well known for coincident current selection, in which substantially all of the conductors in the network are common to a plurality of the stations at the coordinate positions in the matrix, the conductors being arranged between the stations so that each of a number of predetermined combinations of pairs of the read-in conductors corresponds exclusively to a different one of the nine stations in the matrix. This arrangement, interconnecting the bundles of conductors at each station or coordinate position so that each of the bundles constitutes a distinctive combination of the interconnected conductors, is achieved in most of the matrix, as illustrated in FIG. 4, by separating the conductors as they emerge from the bundles and soldering their ends to an appropriate one of the conductive islands 42, 43, or 44. Reference to FIG. 4 will show that the conductor shown to the right in each bundle, such as the conductor 12, is connected at its upper end to the island next above the station and at its lower end to the island next below the station, while the conductor shown to the left in each bundle, such as the conductor 13, is connected at its left end to the island to the left of the bundle and at its right end to the island to the right of the bundle.

An exception has been made, however, in the first column, where the connections in the upward and downward directions have been made directly between the upper and central stations and between the central and lower stations without soldering to the intervening islands. These connections are designated 45 and 46 respectively, and indicate that one wire, without joints, passes from the upper terminal island 47 to the lower terminal island 48 in the first column without a break. Using a similar technique, the conductors shown schematically as located centrally in each bundle are soldered at each end to the remaining conductive islands so as to be connected together diagonally from upper left to lower right. Again an exception has been made in that the central, or read-out, conductor in the station common to the second row and first column is connected to the corresponding conductor in the station in the third row and second column by a continuous, unbroken wire 49. By similar methods the entire conductor network may be prefabricated of unbroken wires, without using any islands 42, as indicated hereinbelow.

Individual magnetic cores are provided at each of the stations of this matrix, each such core having the form of a sleeve or wrapping of a flexible thin strip of ferromagnetic material wound compactly for more than one turn on the bundle of conductors constituting the station. These sleeve-shaped cores may take the form of the core 16 shown in FIGS. 1 and 2, and each core is represented schematically by dashed diagonal lines, as at the core 16 in the upper left station. If desired the wound cores may be cemented to the support 41, and soldering lugs or other connection devices may replace the conductive islands 42-44.

Various methods may be used for the fabrication of the conductor-core elements in the magnetic memory matrix illustrated in 'FIG. 4. The elements may be fabricated individually in the form shown in FIG. 1, each element having a plurality of, and specifically three, separated wires protruding at each end for soldering to the conductive island, as shown at most points in the FIG. 4 matrix. The first turn of the wound core may be held to the conductor unit by cement, by slipping between two of the conductors, or simply by friction, and cement on the top turn may be advantageous to prevent unwinding.

Instead of individual fabrication of the elements several cores may be wound on certain common conductors. Considering now the elements at the three stations in the first column of the FIG. 4 matrix, the conductor 12 in the upper station extends continuously as the conductor 45 into the central station and as the conductor 46 into the lower station, emerging to pass as the conductor '51 to the terminal island '48 at the lower left. As before noted, the read-out conductor 49 also is common to two magnetic elements. Thus, the conductors 12, 45, 46, and 51 and the conductor 49 are woven together, so to speak, with the other conductors illustrated as passing through the several stations at the left of the matrix, and the core strip can be applied in the same operation around the bundles at the several stations in the first column. Accordingly, in forming the bundles in this column the continuous conductor '12454651 is stretched taut, the remaining conductors 11, 13, 49, etc., are placed alongside this stretched conductor, and the core for each station in the first column is fabricated while these conductors are held in place by a suitable fixture. By an extension of these methods it can be seen that the matrix may be built up, one or more stations at a time, by weaving the conductors and assembling the magnetic strips therearound at several stations, for example, one row at a time. When the conductors are woven together and the strips wound therearound one station at a time, starting from top to bottom of the left column and then continuing from top to bottom of each succeeding columns, the array of 'FIG. 4 can be fabricated using continuous conductors for each column, each row, and each diagonal read-out line without ever threading or passing a magnetic strip through a closed space.

Still another method is to build up the entire network of insulated conductors first with the conductors properly bundled together at each station, then to pass the individual core strips down on one side of each station and up on the other to form the sleeve at each station. It is evident that these methods can produce readily a conductor network of the desired configuration in which substantially all of the wires are continuous and unjointed in passing between the sides of the matrix. Whether or not such continuous conductors are used or formed, it will be seen that a network of mutually insulated conductors can be preformed for the entire matrix using any convenient wiring or conductive circuit techniques, including the gathering together of certain ones of the conductors in groups or bundles at the coordinate positions or stations of the matrix and the arranging of the conductors between the stations so that substantially all of the conductors are common to a plurality of the stations and so that the groups of conductors are made up of a multiplicity of different predetermined combinations of conductors corresponding to individual ones of the stations, as is the case with the conductor network in a matrix designed for coincident current selection, such as the matrix illustrated in FIG. 4.

To complete the specific read-out circuit shown by way of example in FIG. 4, external connections are made so that the diagonal connections of read-out conductors are joined together in known configuration to effect a substantial cancellation of noise signals. Starting from one terminal 52 of the read-out circuit, which is grounded, these connections are made by the conductors 53 at the right side of the matrix, 54 at the upper left of the matrix, 56 at the lower right of the matrix, and 57 at the left of the matrix, making the island 58 the ungrounded terminal of the read-out circuit. It will be appreciated that these connections alternatively might be formed by etched circuit conductors between the respective islands on the support 41.

Of course, many variations of the FIG. 4 arrangement are possible, depending on such factors as the size of the array, the method of choosing the particular station, the detailed physical structure of the components, and the physical arrangement of the components. For example, a 16 by 16 array may be divided into rows 1-8 and rows 916. When this is done the read-out conductors, instead of being connected diagonally, may be placed in vertical columns alongside the vertical read-in conductors. Thus a pair of conductors, side by side, would follow the pattern of the conductors 12, 45, 46, and 51, and this pair would extend together vertically through eight rows. The read-out conductor pattern for the two sets of eight rows each then might be connected such that the noise current, or vestigial signals from unswitched cores, gen- 1'0 erated in the upper half of each column flows in the opposite sense to the noise current generated in the lower half of each column. The connections also are made such that the noise current generated in the upper half of the first column flows in the opposite sense to that generated in the upper half of the second column, and this pattern is continued alternately in the succeeding columns. In this case half of each column may be constructed by stringing the continuous vertical read-in conductor and the read-out conductor side by side, placing the horizontal read-in conductors at each station, and then winding eight cores at a time, using a suitable fixture. This procedure greatly simplifies the construction of the array, since only the terminal connections for each row and column, the connections within the array along the rows only, and the connections between the upper and lower halves need be completed after the 8-core half-column units are fabricated.

To illustrate several possible arrangements of the individual magnetic elements and their fabrication individually or in groups, reference is had to the plan view of FIG. 5, illustrating a series of three elements having successive individuad strip-wound cores 91, 92, and 93 wound on the wires 11, 12, and 13. Although the wires 12 and 13 have been cut at several places, their original continuity can be traced from one side of the figure to the other. The group of elements can be made from three continuous wires, or shorter lengths of some of the wires can be bundled together at each of the stations and the three cores fabricated with a single production setup. At the core stations a cross-sectional view would resemble FIG. 2.

If the wire 11 were cut between the cores 91 and 92, the

element on the left would be suitable for insertion individually at any of the stations in the matrix of FIG. 4; note the cross-over of the conductors 12 and 13 at the left of FIG. 5 which permits the read-in conductors to continue vertically and horizontally along their respective column and row, as seen schematically at the lower right portion of each station in the FIG. 4 matrix. One, both, or all of the wires may be cut between the cores 92 and 93, as at the dotted line 94, as required for the arrangement in which the core is to be assembled.

As indicated hereinabove, when storage element selection by coincident currents in the conductor unit is not involved, the arrangement of FIG. 6 may be used, in which each individual bistable magnetic storage device has a single wire 11' and a sleeve of a strip-shaped length of ferromagnetic material which extends continuously around the wire in wound conformation, likewise shown as a spiral 16 of more than one turn, and which is supported by and lies contiguous to the periphery of the wire 11'.

When it is desired to prefabricate the larger conductor network needed for an entire matrix, various wiring techniques may be used, such as the weaving, preforming, or soldering procedures indicated in FIGS. 4 and 5 and additionally in the description hereinabove. Thereafter, as further indicated hereinabove, a core element of ferromagnetic material may be formed surrounding each of the groups of conductors at the individual stations of the matrix. It will be appreciated readily that substantial economies can be effected when, in accordance with the invention, cores of any material or structure giving deoperations or by using various techniques available to the art. The fabrication may be carried out, for example, by using a wrapping tool or head in the form of a short rotatable cylinder having a radial slot aligned parallel to the axis of the cylinder and extending from its surface down to its axis, the slot being just wide enough to receive each bundle of wires at the largest diameter of the bundle. The middle of a length of magnetic strip conveniently may be passed under one wire of the bundle of wires to anchor the middle of the strip to the bundle, leaving both ends of the strip protruding together tangentially from the bundle. The wrapping head then is applied to the bundle by pushing the slot over the bundle until the bundle is seated at the bottom of the slot with the ends of the magnetic strip protruding through the slot. Rotating the wrapping head about its axis then causes the walls of the slot to urge the two halves of the strip together progressively around the bundle in successive spiral turns until the end portions of the strip lie flat at the top of the spiral core. A number of such wrapping heads may be applied simultaneously, for example, to form all of the cores in one row of the matrix. A fixture for holding the conductors during core fabrication might utilize the support 41 itself, having the islands 43 and 44, but with its central portions cut out.

Many circuit arrangements for utilizing the FIG. 4 array in a nine bit, coincident current memory are known to those skilled in the information storage art. An elementary type of such equipment is illustrated in block form in the lower part of FIG. 4. Horizontal switching circuits, unit 61, connect horizontal pulsing circuits, unit 62, effectively through a multiposition switching arrangement 63 in the unit 61 to each of the three rows in the array by means of respective connections 64, 66, and 67. Similarly, vertical switching circuits, unit 68, connect vertical pulsing circuits, unit 69, eifectively through a multi-position switching arrangement 71 in the unit 68 to the ungrounded end of each column in the array by means of respective conductors 72, 73, and 74. An address-selecting device 76, coupled to the units 61 and 68, controls the positions of the switches 63 and 71 to choose a row and a column and thus to determine which of the nine stations in the array is chosen. A timing and read-in control circuits unit 77 is coupled to the horizontal and vertical pulsing circuits, units 62 and 69, as well as to the address-selecting device 76. A connection for input information pulse signals of either positive or negative polarity is provided from a double pole switch 78 to unit 77. The ungrounded end of the read-out circuit in the array at terminal 58 is connected to the read-out gating circuits unit 79 through a conductor 80, and the read-out connections are completed from the unit 79 through a conductor 81 to a read-out utilization device 82. The read-out gating circuits unit 79 also is under the control of the timing unit 77 by virtue of an interconnection 83.

In operation, the address-selecting device 76 determines the effe ctive position of the switches 63 and 71 in the horizontal and vertical switching circuits 61 and 68. The timing and read-in control circuits 77 then trigger the horizontal and vertical pulsing circuits 62 and 69 to develop pulses corresponding to the information to be stored at the station of the array chosen by the switching circuits. The pulsing circuits, of course, are controlled by external connections to the unit 77, which permits pulses to be developed in the pulsing circuits only when a signal is to be recorded; such a positive pulse signal conventionally represents a binary one, while the lack of such a signal represents a binary zero. Alternatively, the external connection to the unit 77 may be made through the double pole switch 78, the lower point of which, instead of being connected to ground, is connected to a source of a negative pulse, thus simplifying the control of the units 62 and 69 to switch the chosen core through the point 23 to the stable negative point 31, representing binary zero, as illustrated in FIG. 3.

The circuits represented in FIG. 4 are connected as if the address-selecting device 76 had selected the first row and first column, as may be determined by following the connections through the switches 63 and 71. When a binary one is to be stored in the corresponding magnetic element, the pulsing circuits 62 and 69 simultaneously develop positive pulses under the control of the unit 77, in turn controlled by the input to the switch 78. The pulse of positive current from the unit 69 passes through the switch 71 and conductors 72, 51, 46, 45, and 12 to be grounded through the terminal 47 at the ground point 84, which is common to the vertical circuits. The unit 62 similarly provides a pulse of positive current through the conductor 64 and thence from right to left along the upper or first row through the conductor 13, whence the current passes through a terminal 86 to a ground point 87 which is common to the horizontal circuits. Each of these current pulses has an amplitude somewhat greater than half that necessary to switch the direction of the residual flux in the core 16, which thus is placed in its stable positive condition 28, corresponding to the binary numeral one, assuming the core has the characteristic represented by the dashed line curve in FIG. 3. If, now, it is desired to change the stored information to a binary zero, the switch 78 is thrown downward to provide a negative pulse. Then the current through each of the read-in conductors 12 and 13 may have a value corresponding to the field intensity 29, so that the net intensity, which thus is double the intensity 29', has a value greater than the saturation value 26', whereby the core is switched to its stable condition 31' representing the binary numeral zero. It will be understood that any of the nine magnetic elements in the matrix may be chosen by suitable positioning of the switches 63 and 71, under the control of the unit 76, at the time the read-in pulses are developed.

During a read-out period, assuming the address-selecting device 76 again chooses the first row and first column, the read-out gating circuits unit 79 under the control of the timing unit 77 is then gated open, and pulses of predetermined polarity from the pulsing circuits 62 and 69 cause the core 16 either to switch back to its binary zero state, or not to switch if it already was in that state. Thus there is developed a signal voltage which is sensed by the read-out utilization device 82, when the core is switched, to indicate that a predetermined binary number had been stored in the chosen magnetic element. Accordingly it appears that the three wires in the element at any station of the matrix, by virtue of their respective connections to the horizontal switching circuits 61, the vertical switching circuits 68, and the read-out circuits 79 and 82, serve individually as a row-selecting wire, a columnselecting wire, and a bistable-state-sensing wire, the three wires at each station constituting a distinctive combination as described hereinabove. Conventional circuit arrangements, not shown, may be provided to switch the core back to its previous state whenever the read-out pulse causes it to change from one stable state to the other, so that the reading out is not destructive.

Many alternative read-in and read-out arrangements are familiar to those skilled in the art. Coincident current arrays are not limited to double coincidence; more than two read-in conductors may be provided at each station of the array. A discussion of the various combinatorial systems possible may be found in a paper by J. A. Rajchman, Static Magnetic Matrix Memory and Switching Circuits, RCA Review, vol. 13, No. 2, pp. 18320l (June 1952). In every case, however, there is coupled to at least one of the conductors means for effecting magnetic saturation in the ferromagnetic material and thus for switching the material from one to the other of its alternate bistable remanent states when information is to be stored. More specifically, such means is provided for passing at a given time sufficient current through at least one conductor in the conductor unit of the magnetic element to provide in the core or ferromagnetic strip material of the wound sleeve 16 the corresponding predetermined magnetic field intensity greater than the aforementioned coercivity value in its hysteresis loop characteristic (as at point 32 in FIG. 3) and sufficient to switch the core and produce a remanence approaching the retentivity value, that is, to produce a magnetic flux approaching magnetic saturation in the sleeve.

In the arrangement illustrated in FIG. 4, this means includes the horizontal and vertical coincident current pulsing and switching circuits 61, 62 and 68, 69 under the control of the timing unit 77 and the information input channel 78. Stated differently, these pulsing and switching circuits provide circuit means connected to at least one of the conductors of a selected core in the matrix for effecting magnetic saturation of the core sleeve material, which has an essentially square magnetic hysteresis loop characteristic as explained hereinabove in connection with FIG. 3.

Alternative coincident selection arrangements are familiar. For example, individual pulsing circuits may be provided for each row and each column of the array with switching arrangements for effectively triggering the pulse generators in only the desired row and column. Attention may be called to the above-mentioned paper by Rajchman and to another paper by the same author, entitled A Myriabit Magnetic-Core Matrix Memory, Proceedings Inst. Radio Eng, vole 41, No. 10, pp 1407-1421 (October 1953), for additional references and for more detailed information regarding arrangements of these types.

While there have been described what at present are considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention. It is aimed, therefore, in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.

What is claimed is:

1. The method of fabricating a magnetic memory matrix including a plurality of magnetic element stations at coordinate positions in said matrix, comprising: forming a network of mutually insulated electrical conductors for said matrix, including the gathering together of certain ones of said conductors in groups at the different stations of said matrix and the arranging of said conductors between said stations so that substantially all of said conductors are common to a plurality of said stations and so that said conductor groups are made up of a plural number of different predetermined combinations of conductors corresponding to individual ones of said stations; and thereafter wrapping a flexible tape of ferromagnetic material around each of said groups of conductors at the individual stations of said matrix.

2. The method of fabricating a magnetic memory matrix including a plurality of magnetic element stations at coordinate positions in said matrix, comprising: forming for said matrix a network of mutually insulated electrical conductors substantially all of which are formed to be continuous and unjointed in passing between the sides of said matrix, including the gathering together of certain ones of said conductors in compact bundles of substantially straight and parallel lengths at the stations of said matrix and the arranging of said conductors between said stations so that substantially all of said conductors are common to a plurality of said stations and so that said bundles are made up of a plural number of different predetermined combinations of conductors corresponding to individual ones of said stations; and thereafter compactly wrapping a flexible strip of ferromagnetic material, having a substantially rectangularly shaped hystere sis characteristic, for more than one turn around each of said bundles of conductors to form a bistable magnetic memory element closely surrounding each such bundle at the individual stations of said matrix.

3. The method of fabricating a magnetic memory matrix, comprising: forming a network of conductors for said matrix, including the gathering together of certain ones of said conductors in groups at the coordinate position stations of said matrix and the arranging of said conductors between said stations so that substantially all of said conductors are common to a plurality of said stations and so that said groups are made up of a multiplicity of different predetermined combinations of conductors corresponding to individual ones of said stations, the conductors in said group at each of said stations being disposed in parallel substantially contiguous relation to each other, but thin bodies of nonconductive solid material being maintained therebetween in sufiicient thicknesses to assure that said conductors remain mutually electrically insulated under conditions of use; forming a bistable core element, having an essentially square magnetic hysteresis loop characteristic, of ferromagnetic material extending closely around, and directly on, each of said groups of mutually insulated conductors at the individual stations of said matrix, and thereafter mounting the preformed memory matrix upon a supporting member.

4. The method of fabricating a magnetic memory matrix, comprising: forming a network of conductors for said matrix, including the gathering together of certain ones of said conductors in compact bundles of substantially straight lengths at the coordinate position stations of said matrix and the arranging of said conductors between said stations so that substantially all of said con ductors are common to a plurality of said stations and so that said bundles are made up of a plural number of different predetermined combinations of conductors corresponding to individual ones of said stations, said sub-' stantially straight lengths of the conductors in said bundles at each of said stations being disposed in parallel substantially contiguous relation to each other, but thin nonconductive coatings being maintained therebetween in suflicient thicknesses to assure that said conductors in said bundles remain mutually electrically insulated under conditions of use; and thereafter forming a core element, having an essentially square magnetic hysteresis loop characteristic, at each station of the matrix by wrapping a flexible strip-shaped length of ferromagnetic material for more than one turn continuously and closely around, and directly on, said bundle of mutually insulated conductors at the individual station.

5. The method of fabricating magnetic core assemblies comprising combining a plurality of insulated conductors into the form of a cable, severing less than all of said conductors into segments, and winding a magnetic tape core tightly around said conductors at each of said segments so formed.

6. The method of fabricating magnetic core assemblies comprising combining a plurality of insulated conductors together along their lengths, cutting less than all of said conductors into segments, and winding said conductors and segments so formed with magnetic tape to form a magnetic core at each of said segments.

7. The method of fabricating magnetic core assemblies comprising joining a plurality of insulated conductors together along their lengths, cutting less than all of said conductors into segments, winding magnetic tape around said conductors and segments so formed to form a magnetic core at each of said segments, heat treating each of said cores, and connecting the ends of said conductors and segments to circuit elements.

8. The method of fabricating magnetic core assemblies comprising combining a plurality of insulated conductors in a cable, severing less than all of said conductors into segments, turning the ends of each segment so formed at an angle with the others of said plurality of conductors, winding magnetic tape around said conductors and segments to form at least one magnetic core at each of said segments, heat treating each of said cores, applying said ends to a mounting board having a prearranged circuit means thereon, and connecting said ends to said prearranged circuit means.

9. The method of fabricating magnetic core assemblies comprising, joining a first plurality of insulated electrical conductors together along their lengths, severing at least one and less than all of said conductors into segments, bending an end of each of said segments away from said conductors, winding magnetic tape around said conductors and segments to form a magnetic core at each of said segments, and electrically connecting each of said ends to the other end of the segments of a second plurality of joined insulated conductors.

10. The method of fabricating a chain of magnetic core assemblies comprising the steps of combining together a plurality of insulated electrical conductors, severing into segments at least one and less than all of said conductors, bending the ends formed by severing said at least one conductor away from others of said conductors, winding magnetic tape about all of said conductors at the center of each segmented portion of said at least one conductor, and heat treating said tape to form a magnetic core at each of said segmented portions.

11. The method of fabricating a chain of magnetic core assemblies comprising the steps of, combining together a plurality of insulated electrical conductors along the lengths thereof, severing into segments at least one and less than all of said conductors, bending the severed ends of the segmented conductors away from the others of said conductors, and winding magnetic tape tightly about all of said conductors at the center of the segmented conductors.

12. A method of fabricating a magnetic core structure comprising the steps of grouping a plurality of electrical conducting wires insulated from one another into the form of a cable; cutting one of said wires of the cable into seg ments along the length thereof; bending the ends of said segments to project at angles to the others of said wires; wrapping all of said wires in the cable tightly with magnetic tape at each of said individual segments of the segmented one of said wires, including shearing said tape to the correct length to form a plurality of magnetic cores; and heat treating each of said cores to secure the outer end thereof and to relieve internal strains which might tend to cause eddy currents,

13. A method of fabricating a magnetic core structure comprising the steps of associating a preselected number of electrically insulated wires into the form of a cable; cutting one of said wires of the cable into segments along the length thereof; bending the ends of said segments to project at angles to the others of said wires; wrapping all of said wires in the cable tightly with magnetic tape at each of said individual segments of the segmented one of said wires, and securing said segment ends to a printed wiring board having prearranged matrix circuitry there- 14. The method of fabricating a magnetic core matrix having core stations arranged electrically in rows and columns comprising the steps of forming a plurality of core stations at said row and column locations by placing a plurality of electrical conductors in close but electrically insulated proximity to one another at each said station, arranging said conductors to be disposed parallel to one another for a portion of their length in the region of each said station, interconnecting conductors of said stations to form a first plurality of conductive paths each of which is common to a row of stations of said matrix, and interconnecting conductors of said stations to form a second plurality of conductive paths each of which is common to a column of stations of said matrix, and then forming a magnetic core of ferromagnetic material surrounding the conductors at each of said stations in the region where such conductors are mutually insulated from and parallel to one another.

15. The method of fabricating magnetic core assemblies comprising combining a plurality of insulated conductors into the form of a cable, winding a plurality of magnetic tapes tightly around said conductors at spaced intervals therealong, and in the intervals between the cores severing less than all of said conductors into segments.

References Cited by the Examiner UNITED STATES PATENTS 2,041,147 5/36 Preisach 340174 2,457,806 1/49 Crippa 340174 2,732,542 1/56 Minnick 29-1555 2,814,031 11/57 Davis 340174 2,901,736 8/59 Sylvester 29155.5 3,058,097 10/62 Poland 340174 WHITMORE A. WILTZ, Primary Examiner.

JOHN F. CAMPBELL, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atent No 3,210,828 October 12, 1965 Douglas Ce Wendell, Jro

It is hereby certified that error appears in the above numbered patnt requiring correction and that the said Letters Patent should read as orrected below.

Column 1, line 53, for "elements" read element column 4, line 15, for "continuous" read M contiguous column 5, lines 64 to 68, strike out "relatively steep flux switching region 24 to 21 or regions 21 to 22 and 23 to 24, each preceded by a well defined, relatively steep fluxwsitching region 24 to 21 or 22 to 23 respectively." and insert instead relatively flat, retentive flux-storing or stable regions 21 to '22 and 23 to 24, each preceded by a well defined, relatively steep flux-switching region 24 to 21 or 22 to .23 respectively column 6, line 21, for "respectively," read representing column 8 line 57 for "island" read islands column 10 line 23, for "individuad" read individual column l3 line 30, for "vole" read vol 0 column 15 line 29, strike out the commao Signed and sealed this 28th day of June 1966o (SEAL) Attest:

ERNEST W. SWIDER EDWARD J, BRENNER Attesting Officer Commissioner of Patents 

1. THE METHOD OF FABRICATING A MAGNETIC MEMORY MATRIX INCLUDING A PLURALITY OF MAGNETIC ELEMENT STATIONS AT COORDINATE POSITIONS IN SAID MATRIX, COMPRISING: FORMING A NETWORK OF MUTUALLY INSULATED ELECTRICAL CONDUCTOR FOR SAID MATRIX, INCLUDING THE GATHERING TOGETHER OF CERTAIN ONES OF SAID CONDUCTORS IN GROUPS AT THE DIFFERENT STATIONS OF SAID MATRIX AND THE ARRANGING OF SAID CONDUCTORS BETWEEN SAID STATIONS SO THAT SUBSTANTIALLY ALL OF SAID CONDUCTORS ARE COMMON TO A PLURALITY OF SAID STATIONS AND SO THAT SAID CONDUCTOR GROUPS ARE MADE UP OF A PLURAL NUMBER OF DIFFERENT PREDETERMINED COMBINATIONS OF CONDUCTORS CORRESPONDING TO INDIVIDUAL ONES OF SAID STATIONS; AND THEREAFTER WRAPPING A FLEXIBLE TAPE OF FERROMAGNETIC MATERIAL AROUND EACH OF SAID GROUPS OF CONDUCTORS AT THE INDIVIDUAL STATIONS OF SAID MATRIX. 